The present invention relates to a defrost control apparatus for a refrigeration system, and particularly, when the power supply is cut off during the operation of the refrigeration system, to a defrost control apparatus for controlling a time term to initiate defrost cycles according to the power throwing-in after breaking down power for a long or a short period.
A conventional refrigerator generates much frost on the evaporator because of the fluctuation of the inside temperature falling off on an evaporator. The frost on the evaporator is removed by driving a defrost heater in order to melt it at intervals of predetermined time. At this time, a defrost timer is installed in the refrigerator to control the interval of the defrost cycle.
A typical example of a defrost apparatus as described above is disclosed in U.S. Pat. No. 4,299,095. This patent initiates a defrost cycle upon the occurrence of two sensed conditions by detecting pressure passing through the evaporator and temperature in the evaporator. The defrosting time is determined by the defrost timer.
A conventional defrost apparatus is shown in FIG. 1. It is described as follows referring to FIG. 1. In the case that the timer apparatus is a mechanical timer, when the power supply is cut off during the operation of a refrigerator, the defrost apparatus does not detect the power failure and, furthermore, when the power supply is cut off for a long time, because the refrigerator is in the state of natural defrost during the power failure, even though the frost on the evaporator has been melted during the power failure, the mechanical timers 2 and 3 are still driving. Thereafter, when the power is applied to the refrigerator in restoration of the power, the refrigerator initiates a defrost cycle at the time set irrespective of the power failure by the timer. In spite of no frost on the evaporator, the defrost heater is wastefully driven, so the inside temperature of the refrigerator rises and, furthermore, the refrigerator has the disadvantage that it wastes power due to a wasteful operation of defrost.
In the case that the defrost timer apparatus is an electrical apparatus, the timers 2 and 3 receive reset signals in a short term as well as in a long term of power failure, so they are initialized. When power is again applied to the refrigerator after restoration of power, the compressor driving portion 4 is driven and the timers 2 and 3 start counting a predetermined time (for example, normally 6 hours). After the predetermined time lapes, the refrigerator operates in the defrost mode. When the power supply is cut off before the defrost time, a defrost timer starts again from the beginning.
Accordingly, the conventional refrigerator has the disadvantage that it misses the time initiating a defrost cycle, so frost forms on the evaporator and the cooling operation is not effectively achieved.
An example to obviate the problems is disclosed in Japanese Patent Publication No. Sho 58-55670. In this patent, cooling operation rate is calculated from the time to terminate a prior defrost cycle. An interval of the defrost cycle adapted to the cooling operation is obtained by multiplying an interval of the defrost cycle in the continuous cooling operation to a predetermined parameter. At power failure, a defrost cycle is forcibly initiated after the lapse of a predetermined time from restoration of power. However, because this patent determines the time to initiate defrost cycle without distinguishing an instantaneous and a long power failure.